The breeding biology of a recently (1974) introduced hedgehog Erinaceus europaeus population was studied on a large Scottish island. These hedgehogs have caused serious declines in internationally important ground-nesting shorebirds, and population control is now being attempted. Sexual behaviour commenced in late April, a few days after the main emergence from hibernation. It peaked in mid-May and again in late June/early July, and ceased by mid-August. Females were promiscuous and were estimated to have sexual encounters (although not necessarily matings) with at least five males during the main mating period. Two-thirds of females attempted to breed for the first time in their second calendar year (i.e. as sub-adults), and the rest in their third calendar year (i.e. as adults). At least 96% (n=27) of adult females attempted to breed in the early part of the season (litters born in June). The vast majority (81%, n=26) bred again in the later part of the season (litters born after mid-July). Breeding success (≥1 young emerged) was relatively high. For adults, 63% (n=24) of early-season and 86% (n=18) of late-season attempts were successful. For sub-adult females the figure was 62% (n=9). The annual mean productivity per female was estimated at 4.04 young for adults and 0.85 young for sub-adults. The implications of these results for the effectiveness, timing and welfare aspects of hedgehog control programmes are discussed.